/*
 * 单利创建
var o1 =  NetWork();
var o2 =  NetWork();
print(identical(o1, o2));  // true
print(o1 == o2);           // true
 * */
class Account {

  static final Account _netWork = Account._internal();//1

  factory Account() {//2
    return _netWork;
  }
  Account._internal();//3

}